Electrochromic display device and method of manufacture

ABSTRACT

An electrochromic display device and method of manufacture is disclosed wherein electrochromic material is deposited in a single layer on a single film of conductive material over the whole area of glass substrate and then the electrochromic material and conductive material are successively etched through a single mask which defines a display segment pattern and remains in position throughout the whole etching process, whereby etched edge portions of the different materials are in excellent alignment and there is therefore small plate area for a reverse emf cell and good display device performance is achieved. The electrochromic material may be etched by the solution employed for developing the photoresist, whereby an etching process step is eliminated.

This application is a divisional, of copending application Ser. No.727,448, filed on Sept. 28, 1976 now U.S. Pat. No. 4,123,841.

The present invention relates to electrochromic display devices andmethods of manufacture. More particularly the invention relates to amethod for electrochromic a required pattern of electrochromic elementsin a simple process.

It is known to constitute a display means by a cell or cells ofelectrochromic material, which is a material in which a normally absentoptical absorption band can be introduced or a normally presentabsorption band can be altered, by application of an electric field orcurrent. A requirement for the electrochromic process is that there bemixed ionic and electronic conduction, and favored materials are thetransition metals or compounds thereof which have the advantage thatthey permit such mixed conduction at room temperature. These materialsare commonly employed in liquid electrochromic systems, in which anelectrolyte is contained between a counter electrode and an electrodewhich has a pattern-defining layer of electrochromic material depositedon the surface thereof which faces the counter electrode and isconnected to an external circuit, electrochromic material in contactwith the electrolyte becoming colored upon application of a negativepulse to the electrode on which it is coated. One substrate andelectrode applied thereon, or both substrates and electrodes, are madeof transparent material to enhance legibility of the display resultingfrom coloration of the different segments of electrochromic material.The pulse applied to cause the electrochromic material to become coloredis generally termed the `activation` or `write` pulse. Application of aso-called `bleaching` or `crasure` pulse, which is a pulse equal invalue but opposite in polarity to the write pulse causes theelectrochromic material to return to its original condition.

A typical example of employment of a liquid electrochromic system isused thereof to define segments 1a of a segmental display unit 1 such asshown in FIG. 1. It is possible to constitute each separate segment 1ain the display unit 1 by an independent electrochromic cell. However, insuch a display unit construction of electrical circuitry becomes rathercomplex, since a separate activation circuit must be provided for eachsegment 1a, and it is therefore practical, particularly in small displayunits, to constitute different segments 1a by different portions of asingle electrochromic cell. For example, in FIG. 1 the display segmentsD1, D2, and D3 lying on the line A-A' are suitably constituted byopposite end portions and a central portion of a single electrochromiccell. According to conventional methods of manufacture such anelectrochromic cell may have a construction such as shown in FIG. 2 orFIG. 3.

In the construction of FIG. 2, a first electrode 2 is applied on asubstrate 1 in segments D1', D2' and D3' which are at least large enoughto respectively define the required pattern of display segments D1, D2,and D3 of FIG. 1. The central segment D2' corresponding to the displaysegment D2 is for example exactly the required size and the outer endsegments D1' and D3' corresponding to the display segments D1 and D3 aresomewhat larger than required size. The first electrode 2 may of coursebe applied as a single layer and then etched or applied directly througha mask to form the segments D1', D2', and D3' for example, or producedon the surface of the substrate 1 in a similar known manner. Next, withthe exception only of outer end portions of the segments D1' and D3',the entire area occupied by and lying between the electrode segmentsD1', D2', and D3' is covered by a layer 3 of a transition metal oxide.The uncovered outer end portions of the segments D1' and D3' serve forconnection of the electrochromic cell to an external drive circuit notshown. After this, layers 4 of insulatory material are applied on thetransition metal oxide layer 3 in line with those portions of theelectrode segments D1' and D3' which are in excess of the electrodelayer area required in order to constitute the display segments D1 andD3. The remainder of the electrochromic cell consists of spacers and acounter electrode not shown, the spacers being provided between andconnecting outer edge portions of the counter electrode and the displaysegment assembly shown in FIG. 2, and electrolyte, which is contained inthe space defined between this display segment assembly, the counterelectrode and the spacers.

In this construction, although the only portions of the transition metaloxide layer 3 required for display purposes are those portions thereofwhich are directly over the portions of the electrode segments D1, D2,and D3, it is necessary that the transition metal oxide layer 3 extendover the whole central area defined by and between the electrodesegments D1', D2', and D3', since if it is attempted by conventionalmethods to apply an individual layer of a transition metal oxide on eachof the segments D1', D2' and D3', there is almost inevitablymisalignment of edge portions of the transition metal oxide layers andthe segments D1', D2' and D3', i.e., at the edge of a transition metaloxide layer and an electrode segment there is produced a step portion,since the transition metal oxide layer covers a larger area than theelectrode segment or vice-versa. This is undesirable, since, as isknown, a transition metal oxide and conductive electrode material incontact with a common electrolyte may in effect constitute electrodes ofan electrochemical reaction and during repeated activation and erasureof the electrochromic material this electrochemical reaction mayconstitute the source of a reverse electromotive force which, if theplate area of the electrolytic cell is sufficiently large, as is thecase when there are step portions at the boundaries of transition metaloxide layers and electrode segments, is strong enough to activate orerase the electrochromic device even in the absence of externallyapplied activation or erase pulses.

Although an electrochromic display device having the construction shownin FIG. 2 avoids this problem, it has the disadvantage that intermediateportions of the transition metal oxide layer 3, i.e., portions of thelayer 3 other than portions thereof directly over the electrode segmentsD1', D2', and D3', are in contact with the electrolyte and also to acertain extent are subjected to electrical fields resulting fromapplication of successive activation and erasure pulses. As a result ofthis, after the electrochromic device has been in use for some time,these intermediate portions become colored, and may be the cause of anerroneous display, it being found extremely difficult in practice torestore the material of layer 3 to its original condition.

To avoid this problem it is known to manufacture an electrochromicdisplay device having the construction shown in FIG. 3, to whichreference is now had. According to this method of manufacture, segmentsof the first electrode 2 which are approximately shaped incorrespondence to and extend at least over the areas to be occupied bysubsequently produced display segments D1, D2, and D3 are evaporated orapplied in another known manner on the substrate 1, and a transitionmetal oxide layer 3 is applied to cover the entire area occupied by andlying between the segments of the electrode 2, with the exception ofouter end portions thereof which serve as external connection terminals.After this the required display segments D1, D2, and D3 are definedbetween layers 4 of insulatory material which are applied over selectedareas of the layer 3 and cover all portions thereof other than portionsat which display is required to be produced. Thus, electrolyte isprevented from contacting layer 3 portions not required for displaypurposes and these portions are therefore not liable to be colored, evenafter prolonged use of the display device. As known, insulatorymaterials do not permit easy production of patterns therein by etchingprocesses, the insulatory layers 4 defining the required display patternmust be applied through a mask. Therefore, since in the current state ofthe art of masking and mask registration there are comparatively greatrestrictions on spacing between adjacent segments, i.e., in this case ondensity of discrete segments of insulatory material, the abovedescribedmethod has the disadvantage that it is unsuited to manufacture ofelectrochromic devices for miniature displays.

It is accordingly an object of the invention to provide a method foraccurate manufacture of electrochromic display devices which areefficient in operation and may include high-density display patternportions.

It is another object of the invention to provide a method forelectrochromic display device manufacture which requires few steps andis easy of application.

According to the invention these and other objects are achieved asfollows. A first substrate and a second substrate are each coated with alayer of conductive material, thereby to constitute a first electrode onthe first substrate and a second electrode on the second substrate. Ifthe electrochromic device is required to be employed in a two-sideddisplay unit both the substrates and both the electrodes are suitablytransparent, or one or both substrates and/or electrodes may be opaqueand have defined therein transparent window portions corresponding todisplay segments. If the electrochromic device is employed in asingle-side display unit, the first substrate and first electrode, forexample, constitute the front of the device and are both transparent,while both the second substrate and the second electrode, or at leastone of these elements constituting the rear of the device, are, or is,opaque. In this case if the second electrode is employed to carrysubsequently deposited electrochromic material, the electrolyte employedin the device is suitably a clear liquid, whereas if the first electrodeis employed to carry the electrochromic material the electrolytesuitably includes a dispersion of barium sulfate, BaSO₄, or similarmaterial to constitute a background for improved viewing of a display.

The material employed for the substrates may be for example glass or asynthetic resin such as polyamide resin, polyester resin, acryl resin,or polyvinyl chloride. Examples of suitable material for the electrodesare indium oxide, In₂ O₃, or stannic oxide, SnO₂, to constitutetransparent conductive films, or precious metals such as platinum, Pt,palladium, Pd, or gold, Au. One of the electrodes, for example thesecond electrode, serves as the counter electrode of the device and insome cases may also be required to serve as a reference electrode also.In such a case, the second electrode may be initially applied as asingle film by evaporation or similar process and then etched so that itis divided into different portions defining the counter electrode andreference electrode, or the counter electrode and reference electrodeportions may be defined directly by depositing the second electrodethrough a mask defining a suitable pattern.

The first electrode applied on the first substrate is left as a singlefilm and has deposited thereon a layer of electrochromic material, whichis preferably the oxide of a transition metal, this being applied byspreading, sintering, evaporation, sputtering, chemical vapourdeposition, or similar known technique.

Next, a mask defining a requisite pattern for production of displaysegments is formed by printing, photolithographic or other known methodon the outer surface of the electrochromic material, i.e., the surfacethereof opposite to the surface in contact with the first electrode, andthen the layer of electrochromic material and the first electrode aresuccessively etched through this mask, the remaining, unetched portionsthereof constituting display segments. Since the outer edge portions ofthe electrochromic material and first electrode assembly are required tobe connected to the counter electrode assembly, the outer edge portionsof display segments are not defined by etched portions but by insulatorymaterial applied on suitable portions of the electrochromic materialsubsequent to stripping of the mask. Since the separate layers ofinsulatory material are provided at comparatively removed locationswithin the display device, there are no problems relating to the spacingbetween the adjacent segments. This display segment assembly isconnected to the counter electrode or counter electrode assembly throughspacers, electrolyte is introduced into the display device, and thedevice is sealed and connected to an external activation circuit.

Since a single mask remaining in the same position is used, fordefinition of display segments, accurate alignment of etched edgeportions of the electrochromic material layer and the first electrode iseasily achieved, step portions at the boundary therebetween areeliminated, and dimensions of display segments may be accuratelycontrolled. Because of this accurate alignment of etched edge portionsof electrode and electrochromic material, both may be allowed to be incontact with the electrolyte since, although there is obviouslyconstitution of electrolytic cells and production of some reverseelectromotive force, the value of reverse electromotive forceproduceable by these cells is extremely small, and can be disregarded incomparison to the electrical value of activation and erasure pulses, asthe plate area defined by the first electrode in any electrolytic cellis effectively limited to the thickness of the first electrode which isonly of the order of 1 μm. In tests conducted it was found thatelectrochromic display devices according to the invention, whileavoiding the abovenoted disadvantages associated with devicesconstructed according to conventional methods, bring about a markedsimplification of manufacturing process, with consequent reduction ofcost involved therein.

The etchant employed in the abovedescribed process need not, of course,be the same for both the electrochromic material and the firstelectrode, but the mask employed must be such that it is unreactive withboth the electrochromic and the first electrode material and also isunreactive with and is not liable to be lifted by etchants employed orsolutions of etched material in the etchants. In the method of theinvention, when electrochromic material employed is a transition metaloxide, particular advantage is gained by use of masks constituted bypositive-type photoresist material, such as the commercially availableproducts of trade names AZ-111 and AZ-119A manufactured by the ShipleyCorporation of U.S.A., or of trade name OFFPR manufactured by Tokyo OkaCo., Ltd., of Japan, for example. In this case, the developer solution,of which there are available various types each corresponding to aparticular type of photoresist, is basic. In contrast to this transitionmetal oxides are acidic oxides, and the developer solution can thereforeact as an etchant with respect to the transition metal oxide layer.Thus, in the development process effected after the transition metaloxide layer has been coated with the photoresist material and has beendried, by maintaining the developer solution in contact with thetransition metal oxide layer after the mask has been defined in thephotoresist material the required pattern can be etched directly in theoxide layer. After this post-baking is effected and the electrode filmetched by a suitable solution. Thus, the process for producing arequired segment-defining pattern is greatly simplified since specialetchant for the transition metal oxide layer is unrequired and set-uptime is reduced.

A better understanding of the present invention may be had from thefollowing full description of several specific examples thereof whenread in reference to the attached drawings, in which like numbers referto like parts, and

FIG. 1 is a plane view showing an example of used of electrochromicdevices in a display unit;

FIGS. 2 and 3 are partial cross-sectional views taken along the lineA-A' of FIG. 1 and showing electrochromic devices construction accordingto conventional methods of manufacture; and

FIG. 4 is a cross-sectional view taken along the line A-A' of FIG. 1 andshowing construction of an electrochromic device according to themanufacture method of the invention.

EXAMPLE 1

Referring to FIG. 4, there was prepared a plurality of electrochromicdisplay devices, procedure in each case being as follows. There wereemployed two glass substrates constituting a first substrate 1 and asecond substrate 8. A layer of indium oxide, In₂ O₃, was deposited ontoone side of the second substrate 8 by evaporation process thereby toform a second electrode 7, which was subsequently divided into separateportions by conventional photoengraving process to constitute a counterelectrode and a reference electrode.

An indium oxide film was evaporated onto one side of the first substrate1 also thereby to form a first electrode 2. Layers 9 of ferro-chrome,Fe-Cr, intended to permit soldered connection of external activationcircuit leads in the completed electrochromic device were evaporatedonto outer edge portions of the exposed surface of the first electrode2. At this stage of the electrochromic device manufacture there is noneed for precise control over dimensions of the ferro-chrome layers 9,since the layers 9 may be subsequently etched to form connection studssimultaneously with etching of the first electrode 2, as describedbelow. This is an advantage in mass-manufacture processes since thelayers 9 may be initially applied in approximately-sized strips alongopposite edge portions or along a plurality of peripheral portions ofthe first electrode 2.

The remainder of the exposed surface of the first electrode 2 was thencovered by a layer 3 of tungsten trioxide, WO₃, deposited by evaporationprocess. The tungsten trioxide layer 3 and the ferro-chrome layers 9were coated with the positive-type resist material which is known underthe trade name of AZ-119A and is manufactured by the ShipleyCorporation, this coat of resist material being applied by spinner.After being dried, the resist material was exposed to a mask patterndefining display segment portions to be formed by the tungsten trioxidelayer 3 and first electrode 2 and external lead connection studs to beformed by the ferro-chrome layers 9.

After exposure the resist material was developed by the developersolution known under the trade name of AZ-303A and manufactured by theShipley Corporation. By maintaining the developer solution in contactwith the resist material longer than usual it was made possible to etchthe required pattern in the tungstem trioxide layer 3 in a singleprocess step. Ferro-chrome being resistant to the developer solutionemployed, the layers 9 were bit etched at this stage. Needless to say,however, the manufacturing process is basically the same if the materialof the layers 9 is conductive and may also be etched by the developersolution employed.

After a time sufficient to complete etching of the tungsten trioxidelayer 3, the developer solution was removed, post-baking was effected,and then, the ferrochrome layers 9 and the first electrode 2 were etchedthrough the same mask by a liquid mixture of ferric chloride, FeCl₃, andhydrogen chloride, HCl. As noted above, outer edge portions of thetungsten trioxide layer 3 and of the first electrode 2 are not etched todefine boundaries of display segments since these outer edge portionsare required to constitute, constructional elements in assembly of theelectrochromic device. Therefore, after stripping of the abovedescribedmask, layers 4 of negative type resist material were applied on outeredge portions of the tungsten trioxide layer 3, the negative resistmaterial employed being the commercially available product known underthe trade name of KMER and manufactured by the Kodak Corporation ofU.S.A., and, in order to facilitate the application process, also beingapplied on the unetched portions of the ferro-chrome layers 9. Thelayers 4 of negative resist material were then exposed to lightprojected through a mask defining the requisite display segmentconfigurations and external connection studs, after which the layers 4were developed, with the result that those portions of the tungstentrioxide layer 3 required for display purposes were exposed and hencecontactable by electrolyte, and other portions thereof remained coveredand protected by the negative resist material of the layers 4, theexternal connection studs also being uncovered. Finally, the first andsecond substrate assemblies were joined by spacers 5, which also definedside walls and which with respect to the electrochromic device werelocated inwardly of the external connection layers 9 and first electrodeportions supporting the layers 9, electrolyte 6 was introduced into thespace defined between the first and second substrate assemblies and thespacers 5 and the electrochromic device, now having the constructionshown in FIG. 4 was sealed. The elecrolyte 4 employed in this examplewas a 10 M solution of lithium prchlorate LiClO₄, in methyl ethylketone, in which solution was mixed a 1:1 by weight addition fo bariumsulfate, BaSO₄, to provide a white background for viewal of theelectrochromic display.

In an electrochromic display device constructed according to the methodof the invention, electrochromic material other than tungsten trioxidemay be employed, examples being molybdenum trioxide, MoO₃, and titaniumdioxide, TiO₂. The electrolyte is suitably constituted by anelectrolytic substance such as lithium perchlorate dissolved to aconcentration of 1.0 m or to saturation in a solvent such as acetone,methyl ethyl ketone, diethyl ketone, methyl propyl ketone, or similarketone, ethyl acetate, isopropyl acetate, n-propyl acetate, or similaralkyl acetate, or 2-ethoxy ethyl acetate, for example the product knownunder the trade name of Cellosolve acetate, diethylene glycol monomethylether acetate, diethylene glycol monoethyl ether acetate, for examplethe product known under the trade name of Carbitole acetate, diethyleneglycol monobutyl ether acetate, for example the product known under thetrade name of butyl carbitole acetate, or similar alkoxy ethyl acetate.If the electrochromic device is employed in a single-side display unit,suitable pigments which are further included in the electrolyte toprovide an improved background for viewal of a display include bariumsulfate, BaSO₄, alumina, Al₂ O₃, titanium dioxide, TiO₂, and Zirconiumdioxide, ZrO₂.

As a specific example, if the resist material employed is AZ-119A, it issuitably applied by roller coater, using Gyrex 9, to a thickness of 3 μ,pre-baked at a temperature of 80° C. for 10 minutes and then exposed for10 seconds, using light emitted by a 3 KW mercury lamp. The developersolution employed for this material is suitably AZ-303A and using thissolution a 2-minute developing process at 25° C. permits etching of thetungsten trioxide layer also. Development is followed by post-baking for20 minutes at 110°, after which the supporting electrode material isetched. If the electrode material is indium oxide the etchant employedis suitably a solution having a specific gravity of 42° Be' ferricchloride, FeCl₃ and concentrated hydrochloric acid, HCl, in a 1:1 ratioby volume. After this the resist material is stripped by means ofacetone.

The material of the insulatory layers 4 applied on the electrochromicmaterial 3 may be a material which is applied by spraying or similarprocess, for example the abovenoted negative-type resist materialmanufactured by the Kodak Corporation and known under the trade name ofKMER, or a resin such as an epoxy resin, for example the product knownunder the trade designation of Epiform R-2401/H160 and manufactured bySomal Industries Incorporated of Japan, a cellulose resin, for examplethe product known under the trade designation of WS-120 and mnaufacturedby the Soken Chemical Corporation of Japan, or a polyvinyl alcoholresin, or a material which is applied by evaporation process, forexample silicon oxide, SiO, silicon dioxide, SiO₂, alumina, Al₂ O₃, ormagnesium fluoride, MgF₂.

The positive type resist applied on the electrochromic material layer 3and external connection layer or layers 9 and employed for production ofa mask defining display segments and external connection studs may befor example any of the products manufactured by the Shipley Corporationand known under the trade designations AZ-111, AZ-119A, AZ-1350,Az-2400, AZ-2415, and AZ-2430, the product known under the tradedesignation of OFPR and manufactured by Tokyo Oka Co., Ltd., or eitherof the products known under the trade designations of ISOFINE SR-30 andISOFINE PR-36 manufactured by the Micro Image Technology Corporation ofJapan. For each of these resist materials there is available a specialdeveloper solution which may be suitably employed in associationtherewith.

Evaporation conditions for deposition of a tungsten trioxide film aresuitably as follows. The evaporation source is a resistance-heatedtungsten crucible, the process chamber is evacuated to a pressure of5×10⁻⁴ torr, substrate temperature is 350° C., and the tungsten film isdisposited at a rate of 10 A per second to a thickness of 5000 A.

Other examples of electrochromic display devices manufactured accordingto the method of the invention are as follows.

EXAMPLE 2

An electrochromic device was manufactured employing a 1.0 m solution oflithium perchlorate, LiClO₄, in propionitrile as the electrolyte,procedure and materials being otherwise the same as for Example 1.

EXAMPLE 3

An electrochromic display device was manufactured employing a 1.0 msolution of lithium perchlorate, LiClO₄, in propylene carbonate as theelectrolyte, procedure and materials being otherwise the same as forExample 1.

EXAMPLE 4

An electrochromic display device was manufactured employing molybdenumtrioxide, MoO₃, as the electrode material, instead of tungsten trioxideWO₃, procedure and materials being otherwise the same as for Example 1.

EXAMPLE 5

An electrochromic display device was manufactured employing siliconoxide, SiO, evaporated through a mask as the material of the layers 4,instead of KMER, procedure and materials being otherwise the same as forExample 1.

EXAMPLE 6

An electrochromic display device was manufactured following theprocedure of Example 5 except that silicon dioxide, SiO₂, was employedin place of silicon oxide, SiO.

EXAMPLE 7

An electrochromic display device was manufactured following theprocedure of Example 5 except that alumina, Al₂ O₃, was employed inplace of silicon oxide, SiO.

EXAMPLE 8

An electrochromic display device was manufactured following theprocedure of Example 5 except that magnesium fluoride was employed inplace of silicon oxide, SiO.

Although the present invention has been fully described by way ofexample, it should be noted that various changes and modifications areapparent to those skilled in the art, it being understood that suchchanges and modifications should be constructed as included thereinunless they depart therefrom.

What is claimed is:
 1. An electro-optical display device comprising:apair of conductive electrodes between which an electric field is to beestablished; said pair of conductive electrodes being formed,respectively, on a first and a second substrate, at least one of saidsubstrates being transparent; a layer of electrochromic materialdisposed in contact with one of said electrodes; said one electrode andsaid electrochromic material layer being segmented to form segmentedareas, said segmented areas including a required segmented displaypattern, the segmented display pattern areas being in contact with saidelectrolyte; the edge portions of said one electrode and saidelectrochromic material layer which are in contact with said electrolytebeing in accurate alignment; and an insulating material layer beingdisposed on and in registry with those portions of said segmented areasexclusive of said segmented display pattern to define the outermostboundaries of said segmented display pattern.
 2. A product comprising anelectrochromic display device manufactured by the method comprising thesteps of:preparing a first substrate assembly and a second substrateassembly, at least one of said substrates being transparent; applying afirst electrode on said first substrate and a second electrode on saidsecond substrate, at least one of said electrodes being transparent andbeing applied on a transparent portion of said substrate, said secondelectrode serving as a counter electrode; applying a layer of transitionmetal oxide material on said first electrode; initially applying saidfirst electrode and said transition metal oxide layer successively onsaid first substrate over an area greater that that necessary to definea required display pattern and an external circuit connection patternthereon; forming mask of photoresist material defining said requireddisplay pattern on said transition metal oxide layer, said photoresistmaterial being characterized such that a developer solution for saidphotoresist material is an etchant solution for said transition metaloxide layer exclusive of the underlying said first electrode layer;etching said transition metal oxide layer and said first electrodethrough said mask, in sequence, with said developer solution and anetchant solution peculiar to said first electrode, respectively, therebyproducing said required display pattern in said transition metal oxidelayer and said first electrode; applying at least one layer ofinsulatory material over those portions of said transition metal oxidelayer which are not required for display purposes; positioning saidfirst substrate assembly and said second substrate assembly in anelectrode facing relationship and joining the assemblies by spacermeans; and introducing electrolyte into the space defined between saidassemblies and said spacer means, said electrolyte being retained insaid space.
 3. A product comprising an electrochromic display devicemanufactured by the method as claimed in claim 2, wherein said mask is aphotolithographic mask constituted by a positive-type photoresistmaterial and wherein said method includes the further step of developingsaid mask with a developer solution acting to etch said transition metaloxide layer to produce said required pattern in a single continuousprocess.
 4. A product manufactured by the method of claim 3, whereinsaid developer solution is alkaline.
 5. A product manufactured by themethod of claim 4, wherein said first electrode is etched with an acidsolution subsequent to the etching of said transition metal oxide layer.6. A product manufactured by the method of claim 2, wherein saidinsulation material is placed on said transition metal oxide layer afteretching of the latter to said required pattern by:stripping said maskfrom said etched transition metal oxide layer and first electrode;applying a negative photoresist material layer over said etchedtransition metal oxide layer and first electrode; exposing said negativephotoresist material to a light pattern corresponding to said requiredpattern; and developing said exposed negative photoresist material toform said layer of insulatory material.
 7. A product manufactured by themethod of claim 6, wherein said mask is a photolithographic maskconstituted by a positive-type photoresist material and including thefurther step of developing said mask with a developer solution acting toetch said transition metal oxide layer to produce said required patternin a single continuous process.
 8. A product manufactured by the methodof claim 7, wherein said developer solution is alkaline.
 9. A productmanufactured by the method of claim 8, wherein said first electrode isetched with an acid solution subsequent to the etching of saidtransition metal oxide layer.
 10. A product manufactured by the methodof claims 2, 3, 4, 5, 6, 7, 8, or 9 wherein subsequent to forming saiddisplay pattern in said transition metal oxide layer and prior toforming said display pattern in said first electrode layer, saiddeveloper solution is removed and post baking is effected.